Global Positioning System Technical Overview. What is GPS? Global Positioning System is: –Satellite based time distribution system 32 Satellites in all.

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Presentation on theme: "Global Positioning System Technical Overview. What is GPS? Global Positioning System is: –Satellite based time distribution system 32 Satellites in all."— Presentation transcript:

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What is GPS? Global Positioning System is: –Satellite based time distribution system 32 Satellites in all numbered 1-32 24 Orbiting satellites in 6 inclined orbits About 12K nautical miles up Each satellite orbits the earth twice every 24 hours When & Why? –1st satellite launched Feb 28, 1978 by DOD –Intended for exclusive military ops: Navigation, positioning, time distribution Consolidate overlapping existing systems Enhance precision weapons delivery –Approved for civilian use in 1980 by President Carter –Each Satellite transmits L1 and L2 signals L1 at 1575.42 MHz is for both civilian and military use L2 at 1227.60 MHz is exclusive to DOD and U.S. Gov (until recently)

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How It All Works The GPS receiver must know two things: –Where the satellites are. (Location of each Satellite) –Time at which the GPS signal was broadcast in order to calculate how far away they are. (Distance to each Satellite) How Does It Know Where They Are? –Each satellite broadcasts its ephemeris model (astronomical position) along with time information and information on the propagation delay through the ionosphere. –The ephemeris model describes satellite position, and velocity at time of transmission. –An un-aided receiver may take 30 seconds to collect the data that repeats twice per minute How Does The Receiver Calculate The Distance To Each Satellite? –Radio waves travel at the speed of light (~ one billion feet/sec) –The distance to a satellite is the time elapsed from transmission to reception times the speed of light. [d = (t 1 – t 0 ) x c] –The receiver uses the time information encoded in the signal to calculate the actual time that elapsed since transmission and then calculates distance. –This process produces fixes with errors on the order of 30 feet –Similarly, the receiver then also knows the correct time to about 30 nanoseconds

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FAQs & More Information FAQs Q: What happens to GPS when users are on a voice call? A: On most current CDMA handsets, voice calls prevent GPS activity. More Information –Wiki Page http://en.wikipedia.org/wiki/Global_Positioning_System#

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